1. Field of the Invention
The invention relates to a method of stabilizing aqueous hydrogen peroxide solutions against decomposition catalyzed by iron and copper in combination.
2. Prior Art
The use of sequestering agents, including salts of various phosphoric acids, to stabilize solutions of hydrogen peroxide for storage or to decrease the tendency of catalysts used to make hydrogen peroxide from its elements to decompose the hydrogen peroxide thus produced, is well known.
It has been proposed by Benckiser, in German Auslegengschrift No. 1,111,604, to employ a combination of three phosphates, sodium pyrophosphate, sodium tripolyphosphate and sodium heptapolyphosphate to stabilize solutions, pastes or suspensions of hydrogen peroxide kept, at pH 5-8, against decomposition. The ternary combination is disclosed as being more effective than either the pyrophosphate or tripolyphosphate or a 1:1 mixture of both.
Riechert, in U.S. Pat. No. 2,027,838, has proposed stabilizing hydrogen peroxide solutions with pyrophosphoric acid, or the product of an acid and tetrasodium pyrophosphate. Preferably, the solutions are kept at pH 1.5-4.5.
It has been proposed by Rust et al, in U.S. Pat. No. 2,871,101, that stabilizers, including oxyacids of phosphorus and salts thereof, improve the yield of hydrogen peroxide formed by oxidation in a non-aqueous solvent. Alkaline-reacting stabilizers, e.g., trisodium orthophosphate, are said to be particularly effective for the treatment of glass vessels usd as reactors, whereas acidic-reacting stabilizers such as H.sub.3 PO.sub.4 or NaH.sub.2 PO.sub.4 are preferred for treatment of aluminum-containing reactors. The reference indicates that ferric, cupric and chromic ions catalyze the decomposition of hydrogen peroxide and that sequestrating hydrogen peroxide stabilizers are selected.
Hooper et al, in U.S. Pat. No. 3,336,112, have proposed the use of various sequestrative stabilizers, including condensed phosphates, for stabilization of aqueous H.sub.2 O.sub.2 solutions, containing an oxygenated organic compound, against decomposition by supported Group I and Group VIII metal catalysts. The stabilizer is also purported to have a specific activating effect on the catalyst by desorbing metal from the support on which it is introduced so as to yield a particularly reactive colloidal form of the catalytic metal.
Izumi et al, in U.S. Pat. No. 4,009,252, have disclosed that various phosphoric acids and salts are stabilizers against iron-induced decomposition, even in the presence of a palladium catalyst.
It has been proposed by Lindner et al, in U.S. Pat. No. 3,194,768, that a combination of pyrophosphate and ethoxylated phenols stabilize acidic hydrogen peroxide solutions. Aromatic sulfonates are disclosed as pH stabilizing agents in this context.
Baum, in U.S. Pat. No. 1,758,920, also has proposed the use of pyrophosphate, in combination with other materials, to stabilize acid-reacting peroxide solutions.
The use of a quaternary stabilizer containing sodium pyrophosphate, straight chain sodium polymetaphosphate containing 12-17 phosphorus atoms and a combination of stannic and polystannic acids, at pH of 5-8, has been proposed by Young (U.S. Pat. No. 3,333,925) for stabilization against combinations including iron, copper, chromium and manganese.
It will be apparent that stabilization of hydrogen peroxide solutions against decomposition catalyzed by metal ions, particularly an iron-copper combination, introduced during preparation in a metal reaction vessel or during dilution with water containing copper and iron ions has been a significant problem, to which a completely satisfactory solution was heretofore unavailable. In particular, the problem caused by the binary Fe-Cu couple commonly present has not been addressed. Although each of Fe and Cu decompose H.sub.2 O.sub.2, the combination of Fe and Cu ions is particularly active in a synergistic fashion. Although the prior art proposes ways in which H.sub.2 O.sub.2 can be stabilized against Fe or Cu- induced decomposition, an effective method of preventing decomposition induced by iron plus copper ions was not previously known.